biological rhythms: infradian and ultradian Flashcards
infradian rhythms - menstrual cycle AO1
cycle is about 28 days soles than one cycle in 24 hours
rising levels of oestrogen cause the ovary to release egg (ovulation)
progesterone helps the womb lining thicken, readying the womb for pregnancy
if pregnancy does not occur the egg is absorbed and the womb lining goes away (menstrual flow)
infradian rhythm
less than one cycle in 24 hours
infradian rhythms - menstrual cycle - AO2 - Stern and McClintock
Studied 29 women with irregular periods
Pheromones were taken from some at different stages of their cycle via a cotton pad under their armpit
These pads were cleaned with alcohol and later rubbed on the upper lip of other participants
68% of women experienced changes in the cycle which bought them closer to the cycle of their ‘odour donor’
infradian rhythms - SAD (seasonal affective disorder) AO1
Is a depressive disorder with a seasonal pattern.
Symptoms are triggered during the winter months when the number of daylight hours becomes shorter
It may be caused by the hormone melatonin:
During the night the pineal gland secretes melatonin until dawn when there is an increase of light
In winter, less light = secretion goes on for longer
Has a knock-on effect on the production of serotonin in the brain
infradian rhythms AO3 - Strength: research on the menstrual cycle shows its evolutionary basis
For ancestors it may have been advantageous for females to menstruate together and become pregnant at the same time
In social groups, this would allow babies who have lost their mothers to have access to breast milk, improving their chances of survival
Suggest that synchronisation is an adaptive strategy
infradian rhythms AO3 -
Limitation: the methodology used in synchronisation studies
There are many factors that may change a women’s menstrual cycle and act as confounding variables e.g stress, diet
Any supposed pattern may occur by chance
May be why other studies haven’t replicated Stern and McClintock’s findings
Suggests menstrual synchrony studies are flawed
infradian rhythms AO3 - Strength: real-world application
Light therapy reduces the debilitating effects of SAD in around 80% of people. Its also safer than antidepressants
However, Rohan et al recorded a relapse rate of 46% over successive winters, compared to 27% in a comparison group receiving CBT
Suggests that light therapy may be an effective short-term treatment but additional treatment may be required if benefits are to be maintained
ultradian rythmn
MORE than one cycle in 24 hours
Stages of sleep - 5 stages
Ultradian rhythms example, the stages of sleep
Sleep pattern occurs in 90 minute periods
Divide into 5 stages, each characterised by a different level of brainwave activity (monitored using EEG)
Ultradian rhythms - the 5 stages of sleep - STAGES 1 AND 2
Right sleep where a person may be easily woken.
In stage 1, brain waves are high frequency and have a short amplitude. These are alpha waves.
In stage 2, the alpha waves continue but there are occasional random changes in pattern called sleep spindles
Ultradian rhythms - the 5 stages of sleep - STAGES 3 AND 4
This is known as deep sleep or slow wave sleep (SWS)
The individual waves now have lower frequency and higher amplitude
Its difficult to wake someone at this point
Ultradian rhythms - the 5 stages of sleep - STAGE 5 (REM)
The brain is paralysed het brain activity closely resembles that of the awake brain.
During this time, the Brian produces theta waves and the eyes occasionally move around, thus rapid eye movement (REM)
Dreams most often experienced during REM, but may also occur in deep sleep.
Ultradian rhythms AO3 - Strength: is understanding age-related changes in sleep
SWS reduces with age.
Growth hormone is produced during SWS is this becomes deficient in older people
Van Cauter et al - suggest the reduced sleep may explain impairments in old age. SWS sleep can be improve using relaxation and medication
This suggests that knowledge of ultradian rhythms has practical value
Ultradian rhythms AO3 - Limitation: is individual differences in stages of sleep
Tucker et al - found large differences between participants in the duration of stages 3 and 4
They suggest hat these differences are biologically determined
This makes it difficult to describe ‘normal sleep’ in any meaningful way
Ultradian rhythms AO3 - Strength/ limitation: lab studies
One of the benefits of conducting studies of sleep in lab settings is control of extraneous variables, such as noise or temperature hat may affect sleep.
However, lab studies involves participants being attached to complicated machinery, so their sleep does not represent eir ordinary sleep patterns
This dilemma means it might be best to conduct some studies in people’s own homes and compare patterns with records made in lab settings.
